The present invention is directed to a compact microwave-powered lamp, which is small and lightweight, and can provide focused light at a small distance from the lamp. The present invention is especially directed to an electrodeless compact microwave-powered lamp, for emitting ultraviolet light. Such a lamp can be used in small devices such as office products (e.g., inkjet printers for the office), and for larger devices, and not only for producing ultraviolet light for industrial applications.
The present invention is also directed to techniques using ultraviolet light or other type of light (e.g., visible light) for curing purposes (for example, for curing ultraviolet light curable inks, or coating materials, or various plastics). This aspect of the present invention is particularly directed to techniques for curing inkjet inks deposited, for example, by an inkjet printer, having utility in many applications including inkjet printers for the office.
Use of microwave-powered lamps for producing ultraviolet light for curing processes is known. It is known to use, e.g., electrodeless, microwave-powered lamps, to produce the ultraviolet light for such curing. However, existing electrodeless, microwave-powered lamps are too large, too heavy and use too much air for cooling, to be considered for some ultraviolet light curing processes. In addition, existing high-powered electrodeless lamps for ultraviolet light curing require an auxiliary ignitor bulb to start the main bulb emitting ultraviolet light, and it is desired to provide an electrodeless lamp that does not require such auxiliary ignitor bulb.
Moreover, existing arc lamps have a short lamp life, and the spectral output changes with use; this is especially true with iron additive lamps. In addition, peak energy focused by the arc lamp is inferior, because the bulb diameter is relatively large for a given power density, and the position of the arc is imprecisely located within the ellipse.
In both arc lamps and existing electrodeless lamps, portions of the elliptical reflector are removed, for air flow purposes, and this reduces the energy being focused by the reflector.
U.S. Pat. No. 5,998,934 to Mimasu et al. discloses a microwave-excited discharge lamp apparatus which emits light by discharge under a microwave electromagnetic field. The structure of this device includes a microwave generator for generating a microwave, a waveguide for propagating the microwave to a cavity resonator unit, and a microwave discharge lamp arranged in the cavity resonator unit, the microwave-excited discharge lamp apparatus including a rotary supporter for supporting the lamp rotatably, and a blow guide arranged around the lamp in the cavity resonator unit for conducting a cooling air to the lamp for cooling the lamp. According to U.S. Pat. No. 5,998,934, the microwave generator and the cavity are provided at opposite sides of the waveguide and at opposite ends thereof, and microwaves from the waveguide are introduced into the cavity through a curved reflector of the cavity-forming member.
In the structure of Mimasu et al., by having the microwave-introducing window (and structure for rotating the bulb) extending through the curved reflector forming the cavity in which the bulb is positioned, a substantial portion of the reflector is removed, whereby the curved portion of the reflector inefficiently reflects the light emitted from the bulb. Moreover, this structure of Mimasu et al., having the bulb rotator, microwave generator and RF cavity positioned so as to include structure on opposite sides of the waveguide structure, takes up a lot of room.
U.S. Pat. No. 5,866,990 to Ury et al. discloses a microwave-powered, electrodeless lamp, utilizing a single rotary motor to rotate the bulb and provide rotary motion to a blower or pump means for providing cooling fluid to the magnetron and/or to a forced gas cooling for providing cooler gas to the bulb. This patent discloses structure wherein the bulb is rotated to provide various advantages including temperature equalization around the bulb surface, improved spatial emission properties, discharge stabilization, elimination of visual xe2x80x9cwobblexe2x80x9d, increased efficiency and better cooling, and provides, for example, cooling of the magnetron used to provide the microwaves. The contents of U.S. Pat. No. 5,866,990 are incorporated herein by reference in their entirety.
U.S. Pat. No. 6,102,536 to Jennel discloses apparatus and a method for printing images on packaging material, including jetting ink through an inkjet print head onto a surface of a web. The printing site includes, inter alia, a printer and a curing device, the printer having at least one print head, for example, an inkjet print head. The curing device, where the inks are ultraviolet light-reactive inks, can, for example, be an ultraviolet light source. This is a typical illustrative example (and not to be limiting) of an environment for use of lamps (e.g., microwave-powered lamps) as in the present invention.
As can be seen from the foregoing, while various microwave-powered, e.g., electrodeless lamps, and also arc lamps, are known, it is still desired to provide microwave-powered lamps having a compact size, which are lightweight, and have stable light (e.g., stable ultraviolet light) spectral output. It is also desired to provide such a lamp which can operate on 120 or 230 volt power (residential or office power, rather than industrial levels), and has low air-cooling requirements. It is desired to provide such compact lamp, which has applicability to smaller devices such as office products. (e.g., inkjet printers). It is also desired to provide a lamp having a compact size and is lightweight, and yet wherein a tubular or cylindrical bulb of the lamp can be rotated.
It is also desired to provide techniques for printing, coating, marking or imaging including curing or drying the printed, coated, marked or imaged structure, using such lamp.
The foregoing objectives are achieved by the lamp structure and method of using such structure, according to the present invention, discussed in the following. Generally, the structure of the present invention includes a microwave generator, a waveguide, and an RF cavity. The RF cavity has positioned therein a bulb, of the microwave-powered lamp. The waveguide is provided for directing microwaves generated in the microwave generator to the cavity (which, as known in the art, is a cavity resonator, for accumulating microwave energy). The cavity is defined by end members and a member extending therebetween (this member extending therebetween being, e.g., curved, and having, for example, a cross-sectional shape of a partial ellipse with an opening at one end). This member extending between the two end members is, desirably, a primary reflecting member forming the boundary of the cavity. The cavity is positioned adjacent to the waveguide such that one of the end members is positioned so as to overlap a side of the waveguide. An RF slot extends from the waveguide through the side of the waveguide, and through this one of the end members positioned so as to overlap a side of the waveguide, into the RF cavity, for introduction of the microwaves from the waveguide into the RF cavity.
By providing the RF slot through the end member (e.g., end reflector) instead of, e.g., the reflecting structure between the end members (e.g., the member having the partial elliptical shape in cross-section), energy focus is improved. In addition, the compact nature of the structure can also be improved.
The cavity is positioned to overlap the side of the waveguide so that the RF slot can extend into the cavity. As can be appreciated, the cavity, extending along the side of the waveguide, can extend beyond the end of the waveguide.
Desirably, another end member defining the RF cavity, opposite the end member having the RF slot therethrough, has an opening therethrough for inserting the bulb into the RF cavity. Here also, by providing the bulb through this other end member, a break in the reflector surface between the end members (that is, the member extending between the end members) is avoided, improving effectiveness of emission of radiation (for example, ultraviolet light) from the lamp.
The structure according to the present invention can also include structure to rotate the bulb in the cavity, providing advantages of such rotation, as discussed previously, in a relatively compact structure.
In addition, the structure according to the present invention can also include structure (for example, but not to be limiting, a fan or blower, or a source of compressed cooling fluid (such as compressed air)) to pass cooling fluid (such as air) by the bulb for forced cooling of the bulb. This cooling fluid passing by the bulb passes through the RF slot in passing into the cavity or passing out of the cavity, providing a compact path for passing of the cooling fluid. Desirably, the, e.g., fan or blower is provided such that the cooling fluid passing by the bulb and through the RF slot also is forced to flow past the microwave generator (for example, magnetron), for also cooling the microwave generator.
Under some circumstances, rotation of the bulb, using the structure to rotate, provides sufficient bulb cooling without the need for additional cooling structure.
According to another aspect of the present invention, the RF slot between the waveguide and cavity is in one end member of the RF cavity, and the bulb of the microwave-powered lamp extends from an opposite end member of the cavity. The bulb is aligned with the RF slot when positioned in the RF cavity, so as to achieve most effective use of the microwave energy for emission of light (e.g., ultraviolet light) from the bulb. For example, this alignment is achieved by a central axis of the bulb (e.g., a cental axis of a tubular bulb), when extended beyond the bulb, intersecting the RF slot (desirably, a center line of the RF slot).
According to other aspects of the present invention, the microwave-powered lamp has a bulb which emits ultraviolet light and/or visible light, of relatively high intensity, and is used for ultraviolet or visible light curing of various materials, such as, but not limited to, paper, plastics, textiles and foils, and curing of inks and coatings of various materials, including inks and various plastics. In one embodiment of use of this compact microwave-powered lamp, the lamp is used as a curing device used in conjunction with a print head of an inkjet printer, for curing ultraviolet light-cured inks deposited by an inkjet printing head. The compact microwave-powered lamp according to the present invention can, for example, be used as a substitute for the described curing device in U.S. Pat. No. 6,102,536. Of course, the lamp according to the present invention is not limited to use in an inkjet printer, but rather has many various uses, including (but not limited to) any printing, marking, bonding or imaging process such as in medical uses, small-part curing and wire marking, packaging, and curing of component electronic structures.
The microwave generator utilized according to the present invention can be a conventional magnetron; for example, the microwave energy can be produced using a 1000 watt consumer oven magnetron. Various relatively small components can be used; for example, the bulb used can be a tubular bulb approximately 50 mm long, the outside diameter thereof chosen varying from 7 mm to 18 mm depending on the power level desired and the cooling scheme used. The waveguide can be small, e.g., very short (e.g., about 4.7 inches long by 2.8 inches wide by 1.7 inches high); and the height of the cavity, and minor and major diameters thereof, and the short waveguide, create compactness of the lamp.
Illustratively, the RF cavity can have a partial elliptical surface between the two end members, with the two end members being spaced 3.0 inches. The elliptical shape of the partial elliptical reflector can have a major diameter of 4.31 inches and a minor diameter of 3.54 inches. These dimensions are examples and are not to be limiting of the present invention.
In addition, according to the present invention, having cooling air at least for the bulb, and preferably for both the magnetron and bulb, passing through the RF slot, a further compact structure is provided, which is relatively quiet, especially for use in an office product (inkjet printer).
As compared to arc lamp alternatives, the microwave-powered lamp according to the present invention provides a stable ultraviolet light output during operation, a longer lamp life and higher peak energy at focus.
Moreover, as compared to alternative electrodeless lamp devices, the present invention provides a lamp of compact size, less weight and low air cooling requirements. Furthermore, the rotating tubular lamp provides for uniform stress along the bulb wall, with respect to both thermal and electric field stresses, as well as other benefits.
In addition, the microwave-powered lamp according to the present invention starts without an ignitor bulb. That is, with structure according to the present invention, sufficient microwave energy can be provided to the RF cavity to create an electric field in the RF cavity which ignites the lamp bulb without the need for an ignitor bulb.
Furthermore, by providing the RF slot on the end member, instead of through the, e.g., elliptical-shaped reflector, energy focus is improved and compactness is also improved. In addition, this structure permits the product focus to be closer to the lamp, for example, 0.38 inches versus 2.1 inches. By providing positioning of the slot relative to the bulb as in aspects of the present invention, effectiveness of use of the microwave energy is improved.
In addition, through use of cooling air flow through the RF slot, according to various aspects of the present invention, the same lamp configuration can be cooled with positive or negative pressure.